Bertram33 User Forum

Hello All Does anyone on this site have Cummins 6bta’s 300 hp in the FBC? Just want to know what size props you are running. Boat is new to me and I’m concerned about over propping the engines. Thanks in advance

You need to know what gear reduction you have . Most of us around here are running 1.5 to 1 and use a 21" dia., 21 or 22" pitch, depending on cup, 3 blade prop. The key is making sure you get at least 2900 RPM at wide open in gear.

I have a 220a with the same gear reduction. The prop is stamped 22x19.5 not sure what the cup is. Michigan Nibral 3 blades. I have not verified tacos for accuracy but the sea trial on alight load they registered 3000. Not sure what the tip-top end speed was. I’m concerned about over propping the 6bta. It cruised nice at around 18-29 mph at 2200 rpm.

That should read 18-20 mph depending on sea condition and wind. Thanks

That should read 18-20 mph depending on sea condition and wind. Thanks

Bob, Mine are ZF 220a 1.5:1. Prop type and size for me are Mich Nibral DJX, 21DX22P with a #5 (aka Med) cup. Cruise is 2400rpms which gives 22-24 knot cruise (25-27.6mph) depending on load and conditions. WOT is a little over 2900rpms. 18-20mph (15.65-17.40 knots) seems a little slow for 2200rpms with the engine and gear combo you mentioned. Hope this helps.

Doug what Hp are you? He is 300 I’m 350 and get 22-23Kts at 2400rpms.

Thanks for the reply. I’ll have to verify my tachs and see if I’m getting all of the performance out of the engines without overpropping.

Tony. I think the Cats are heavier than the Cummins. Doug’s are 300,mine were 330 I got 1 more knot at cruise.